In a principal aspect the present invention comprises a generally neutral, liquid phosphorus containing fertilizer having a significant phosphite ion concentration. Phosphorus acid, ammonia and water properly mixed pursuant to controlled temperature and pH conditions produce a stable phosphite ion containing solution which may be mixed with other fertilizer materials including ammonium phosphates. The invention further relates to methods for preparing such fertilizers and the use of such fertilizers on plants.
Nitrogen, phosphorus and potassium are principal elements found in fertilizer compositions applied as solutions or in granular form to enhance plant growth. A great deal of research and development has focused upon maximizing the efficacious delivery of these elements to plant life. Various compositions incorporating these elements have been patented. For example, Hsu in U.S. Pat. No. 5,707,418 discloses an inorganic phosphorus containing fertilizer comprised of various phosphorus compounds in the form of acids or salts in combination with an inorganic complexing agent. The purpose of the Hsu invention is to provide a highly stable, concentrated phosphorus containing fertilizer, which can be stored for long periods of time yet easily absorbed through the foliage system or the root system of a plant and a process for manufacturing the material. Hsu in U.S. Pat. No. 5,865,870 discloses a phosphorus containing fertilizer, which is a combination of polyphosphoric acid and salts and phosphorous acid, with the goal of obtaining increased phosphorus uptake by plants exposed to this fertilizer. Lovatt, in a series of patents including U.S. Pat. Nos. 5,514,200 and 6,113,665 discloses concentrated phosphorus containing fertilizers that employ buffered compositions or defined mixtures of phosphorus compounds in order to supply phosphorus to plants thereby enhancing phosphorus uptake.
Other patents and publications which relate to such compositions, their manufacture and use, include the following: U.S. Pat. Nos. 5,800,837; 5,830,255; 5,864,418; and Fertilizer Research 32, 161-168 (1992).
Reported research indicates that delivery of the phosphorus element to plant life may be effected by exposure to either a phosphate ion (e.g. H2PO4xe2x88x921) or a phosphite ion (e.g. H2PO3xe2x88x921). Phosphite ion exposure appears to have an advantage when applied in a solution form to the foliation of a plant because it is more readily assimilated than a phosphate ion. Additionally, combinations of phosphite and phosphate ions are believed to be more effective than either alone in plant assimilation and in providing an effective means for controlling plant fungus diseases.
Providing phosphite ion containing fertilizers constitutes a significant challenge. Formulations of phosphite ion containing materials that have been previously suggested as fertilizers are phosphorous acid (H3PO3), and potassium phosphite, (K2HPO3). However, phosphorous acid is a stronger acid than phosphoric acid and is highly corrosive thus diminishing its desirability as a phosphite ion source. Potassium phosphite is an expensive compound typically made by neutralizing phosphorous acid with potassium hydroxide. The reaction is highly exothermic. The heat evolved is a challenging problem since phosphorous acid is very unstable. That is, as phosphorous acid is heated above 180xc2x0 centigrade, then phosphine, PH3, is produced. Phosphine is a highly toxic gas that is spontaneously flammable in air.
As a consequence there is a need for a low cost, safe, efficacious source of phosphorous in the form of a phosphite ion (HPO3xe2x88x922, H2PO3xe2x88x921) that is stable, having neutral or nearly neutral pH and preferably in combination with a nitrogen source. Further, it is desirable to have such a material which can be manufactured utilizing present day, available fertilizer production facilities.
Briefly, the present invention comprises a phosphorus containing fertilizer composition which includes a significant phosphite ion concentration, and in a preferred embodiment, nitrogen and phosphate ions in the form of ammonium phosphates and polyphosphates. The fertilizer is in the form of a concentrated liquid solution which may be diluted, mixed with other plant growth constituents such as urea, etc., and has a pH when in water solution in the range of about 5 to 8, preferably in the range of about 5.5 to 6.5 or about 6.2. In the preferred embodiment, the composition has a nitrogen concentration in weight percent of about 6 to 10 and a phosphorus concentration in weight percent in the form of P2O5 of about 22 to 36. A preferred process for manufacture of the composition utilizes slightly modified ammonium phosphate fertilizer manufacturing facilities to combine phosphorous acid, ammonia and water under controlled conditions of maintaining the temperature below 150xc2x0 F. and the pH generally neutral during batch or continuous process mixing. Mixtures of manufactured ammonium phosphites and species of ammonium phosphates are considered most desirable, particularly when the weight percent of phosphorus (P2O5) from the phosphite and phosphate compounds are about equal. A most preferred composition comprises a 9.8-34-0 ammonium phosphite/ammonium phosphate solution. The compositions demonstrate significantly improved phosphorus uptake.
Thus it is an object of the invention to provide an improved phosphorus source fertilizer composition.
Yet another object of the invention is to provide a fertilizer composition having a significant source of phosphorus in the form of a phosphite ion and further including a significant source for nitrogen.
Yet another object of the invention is to provide a fertilizer composition which may be manufactured utilizing currently available ammonium phosphate facilities wherein the composition contains highly concentrated amounts of the phosphite ion.
Another object of the invention is to provide a safe, cost effective, and easily monitored process for the manufacture of a phosphorus containing fertilizer in liquid form which has a high concentration of the phosphite ion.
Another object of the invention is to provide various methods and formulations for the manufacture of a nitrogen/phosphorus containing fertilizer composition wherein the phosphorus portion of the composition is in the form of a phosphite ion in solution and wherein the solution is neutral or nearly neutral.
These and other objects, advantages, and features of the invention will be set forth in the detailed description that follows.